Phylum protozoa

Defination: unicellular or acellular, eukaryotic and commonly motile organisms are called protozoa.                                            History:1.Leeuwenhock(1676)first gave preliminary accounts of some protozoan forms after the discovery of microscope.       2.Goldfuss(1818)coined the term protozoa but he included many non-protozoan forms under protozoa.                                                     3.von siebold(1845) recognised the unicellular nature of the protozoa and established the term protozoa in its true sense.                                                                      General characteristics features:.                      1.Protozoans are usually microscopic and unicellular individuals. They exhibit all types of symmetry.                                               2.Most species occur as single but many are colonial.                                                                   3.Body is bounded by a cell membrane or plasmalemma. Body may be naked or is covered by a pellicle or a test,made up of silica or calcium carbonate.                               4.A filamentous network of the cytoskeleton may form a dense supportive structure ,called the epiplasm.                          5.Usually uninucleate ,but may be mor than single nucleous in some forms.                         6.Locomotor or organelles may be flagella (e.g Euglena),cilia(e.g paramecium),Pseudopodium(e.g Amoeba),or absent in parasitic forms(contractile myonema are present in the body).                                                               7.Nutrition may be holozoic ,e.g Amoeba(animal like),holophytic( e.g Euglena),saprophytic,mixotrophic or parasitic .                                                                 8.Intracellular type of digestion occurs with in the food vacuoles.                                   9.Respiration performs generally through the outer surface of the body .but may be few facultative or obligatory anaerobes.        10.Excretion performs generally through the body surface,and water regulation of the body is accomplished by contractile vacuoles.